Means for adjusting field strength in electromagnetic devices



Jan. 23, 1934. R. D. SLALMON 1,944,578

MEANS FOR ADJUSTING FIELD STRENGTH IN ELECTROMAGNETIC DEVICES Filed Feb.25, 1931 REGINALD o. SALMON BY- ,1: .2/ .20 27 32 a ATTORNEY PatentedJan. 23, 1934 PATENT OFFICE MEANS FOR ADJUSTING FIELD STRENGTH INELECTROMAGNETIC DEVICES Reginald Dennis Salmon, Oroydon, England,assignor to Creed and Company, Limited, Groydon, England ApplicationFebruary 25, 1931, Serial No. 518,120, and in Great Britain March 26,1930 6 Claims.

This invention relates to a method of and means for adjusting magneticfield strength in electromagnetic devices such as relays in which apermanent magnet is employed to provide a magnetic flux.

The object of the invention is to provide a simple means for readilyvarying the field strength of a polarized relay such as that disclosedmore particularly in Patent No. 1,864,296, issued to F. G. Creed et al.on June 21, 1932, and also described on pages 256-251 of Telegraphy byT. E. Herbert, published by Sir Isaac Pitman & Sons, London, 1930. Theinvention is applicable, however, to other classes of apparatus as willbe readily seen from the following description.

In polarized electromagnetic relays for example, a strong magnetic fieldresults in firm contact pressure of the movable contact stops upon thefixed contact stops upon actuation of the relay armature. A disadvantageof a strong magnetic field is that a relatively heavy current isrequired to overcome this contact pressure and to eiiect the actuationof the movable armature from one stop position to another. If the fieldstrength is reduced the relay is rendered more sensitive to weakactuating currents but this is accomplished at the expense of reducedcontact pressure. In such relays, as in other cases, it is a greatadvantage to be able to adjust the effective field strength in a readymanner, by the simplest means possible. One method and means ofadjusting the field strength of a relay is disclosed in theabove-mentioned patent. The present invention involves an improved andnovel method for more effectively controlling the field strength of arelay or similar apparatus.

The invention consists in a method and means for adjusting fieldstrength in electromagnetic devices of the class referred to. Itaccomplishes this result by tilting a permanent magnet by means of anadjusting screw from off the faces of two soft iron pole pieces or fixedmembers of the magnetic circuit, each of these members being similarinshape and approaching each other so closely as to form a substantiallyclosed magnetic circuit. The permanent magnet is therefore, held tothese pole pieces by magnetic attraction. The tilting action exposes thefaces of the pole pieces and causes a wedge-shaped air gap to be formedbetween the pole pieces and the formerly contiguous sides of thepermanent magnet, one edge of each of the ends of the permanent magnetremaining in continuous contact with its immediately associated polepiece. In this manner an adjustable wedge shaped airgap is formedbetween the faces of the pole pieces and the surfaces of the permanentmagnet previously contiguous to those faces.

Referring to the accompanying drawing:

Fig. 1 shows diagrammatically the method of semi-circular permanentmagnet for the bar magnet indicated by numeral 12 in Figs. 1 and 2 ofthat mentioned patent. Further constructional details are also given inthis mentioned patent. These details are not shown in the presentapplication as it is not deemed neces- (0 sary to uselessly encumber thedrawing with features which are not especially subservient to thecomplete operation of the apparatus involved in this application.

Figure 3 shows, in front elevation, a relay in which adjustment iseffected in accordance with the present invention.

Figure 4 is a side elevation of the relay shown in Figure 3 with thecover thereof in section.

Referring first to Fig. 1, this shows in diagrammatic representation apole piece 2 of magnetic material, such pole piece being one of a pairof pole pieces adapted to be permanently energized by a permanent magnet1 placed in contact with their end faces. The permanent magnet, which ispreferably of semi-circular shape, is held against the ends of the polepieces solely by magnetic attraction. Other pole faces of the polepieces co-operate with a moving armature of the magnet system in anysuitable manner, for example as will be more fully hereinafter describedin connection with Figs. 3 and 4.

Threaded in a suitable portion of the apparatus, here shown as bracket'7 attached to the casing 6 of the relay, is an adjusting screw/i whichmay conveniently be turned by head 5, the point of the screw bearingagainst the extended semi-circular U-shaped yoke portion of thepermanent polarizing magnet 1.

By turning the adjusting screw 4 the magnet 1 can be tilted away fromfull contact with the pole piece faces 2 and 3 of the fixed members.This results in the formation of a thin wedge shaped air gap in themagnetic circuit which in turn causes a reduction in the magnetic fluxin the latter. The edges of the poles at the further extremities of themagnet 1 will however be held in contact with the further edges of theend faces of the pole pieces by magnetic attraction, the contactingelements being reduced. from two contiguous surfaces to two contiguouslines. The attraction will also cause the magnet to follow screw 4 onretraction of the screw 4 in order to reduce the angle of the air-gap inthe wedge shaped opening between the surfaces.

The application of the invention to an electromagnetic relay similar tothat described fully in said Patent No. 1,864,296 previously referredto, is shown in Figs. 2, 3 and 4. Magnetic pole pieces 2 and 3 havingoppositely facing upper extremities 21, 22 and similarly facing lowerextremities 23, 24 are moulded into a carrier 8 of insulating material.The pole pieces 2 and 3 are, therefore, [-shaped. The upper and lowerextremities of these pole pieces form two polar gaps in which anarmature rocks on an horizontal axis on pivots fixed to the carrier 8 ata position 25 mid-way between the two gaps. Opposite ends 26 and 27 ofthe armature move from one side to the other in the upper and lower gapsrespectively. The armature carries an extension 28 on the extremity ofwhich a contact 11 is adapted to play between contact screws 12 and 13as actuated by the armature. An actuating coil or coils 14 surroundingthe armature, but separated therefrom, is or are clamped to the carrier8 by suitable means. The carrier 8 with the pole pieces 2 and 3, coils14 and the pivoted armature form a unit which is pivotally mounted bypivot 9 to a vertical standard 29 formed of moulded insulating materialin one piece with a base portion 30. The vertical standard 29 carriesextensions 31, 32 in which the contact screws 12 and 13 respectively aremounted. The base portion 30 carries a bias adjusting screw 10 with thepoint of the screw engaging an extension (not shown) of the carrier 8 tomove it on pivot 9 against spring means (also not shown) whereby themagnetic bias of the relay can be readily adjusted, as is fullyexplained in said U. S. Patent No. 1,864,296.

The pole pieces 2 and 3 are magnetized to 0pposite magnetic poles by apermanent magnet 1 which is held only by magnetic attraction of theextremities of the magnet 1 to horizontal exposed end faces 31 and 32 ofthe pole pieces 3 and 2 respectively. The bow-shaped mid-portion ofpermanent magnet 1 extends in a forward direction and is engaged on itsupper surface by an adjusting screw 4. This screw 4 is rotatablysupported at its upper end in a bracket 33 fixed to a circular casing 6of the relay and threaded at its lower end in a second bracket 7 alsofixed to casing 6. The casing 6 is provided with a cover 34 hinged at 35to permit ready access to the contact screws 12 and 13, and to a head 5of the adjusting screw 4.

It will be seen that the magnetic circuit or circuits in the abovedescribed relay forms or form what is known as a balanced armaturemovement. In accordance with the direction of current in the coil orcoils 14 the direction of flux along the armature and the distributionof the magnetic flux from the permanent polarizing magnet 1 is alteredin the upper and lower gaps in which the ends of the armature oscillate.

The contact 11 is thus actuated from one to the other of contact screws12, 13 and is held against the respective screw owing to the permanentmagnetic flux from magnet l causing the attraction of the ends 26, 27 ofthe armature to the nearer pole faces in the two polar gapsrespectlvely.

The relative attraction to the nearer pole face of the armature when inone position as compared with that in the other can be adjusted byvarying the position of carrier 8 by screw 10, as previously mentioned.The total force by which the armature is held in either position,disregarding any force due to the actuating coil 14, can be adjusted inthe present arrangement by screw 4. In Figs. 3 and 4 screw 4 is showntilting permanent magnet 1 on the horizontal faces 31, 32 of the polepieces 3 and 2 against the magnetic attraction of the magnet to the polepieces. The wedge-shaped air gap, which is best seen in Fig. 4,introduced into the magnetic circuit, reduces the total flux in the polepieces and thus increases the sensitivity of the relay. If screw 4 isturned by head 5 to raise the screw, the air gap is reduced as magneticattraction causes magnet 1 to follow the screw 4. The total flux in themagnetic circuit is increased and results in a correspondingly greaterpressure of the movable contact 11 on either contact stop 12 or 13. Aspreviously mentioned, however, this necessitates a heavier currentthrough the actuating coils 14 to eifect the actuation of the armatureto the opposite position.

The screw 4 provides a ready and simple method by which this adjustmentcan be made and it will be seen that if the end of screw 4 bears on asmooth portion of the upper surface of magnet 1 the bias adjusting screw10 can be altered without affecting in any appreciable manner theadjustment due to screw 4.

Although the invention is particularly applicable to electromagneticrelays it will be appreciated by those familiar with the art that it isalso applicable to other electromagnetic devices in which it isdesirable to provide means for readily varying the field strengthproduced by a permanent magnet in those devices.

What is claimed is:

1. In an electromagnetic device such as a polarized relay, means foradjusting field strength comprising in combination, relatively fixedpole pieces having exposed faces, a permanent magnet held on to saidfaces by magnetic attraction, and an adjusting screw bearing against anextension of said magnet to tilt it against said magnetic attraction onsaid faces to introduce a wedge shaped air gap therebetween.

2. In an electromagnetic device such as a polarized relay, tworelatively fixed pole pieces each having an exposed face, asemi-circularly shaped permanent magnet held by each pole thereof to oneof the exposed faces of said pole pieces respectively, and an adjustingscrew bearing against the yoke portion of said permanent magnet.

3. An electromagnetic polarized relay comprising in combination, twopole pieces, a carrier of moulded insulating material in which said polepieces are imbedded, leaving an exposed face on each, a semi-circularlyshaped permanent magnet held by the magnetic attraction of each polethereof to one of the exposed faces of said pole pieces andsubstantially at right angles to said carrier of insulating material,and an adjusting screw bearing against the laterally extending yokeportion of said permanent magnet.

4. An electromagnetic device such as a polarized relay, comprising apair of pole pieces, a permanent magnet having, and rotatable about, anedge in contact with said pole pieces, and means for rotating saidmagnet about said edge.

5. Electro-magnetic apparatus of the type herein described, comprisingtwo oppositely arranged [-shaped pole pieces, a carrier of moulded tiontwo [-shaped pole pieces, a support of moulded insulating material forsaid pole pieces, each of said pole pieces having an exposed surface, apermanent magnet each pole of which is held to one of the exposedsurfaces of the pole pieces by the magnetic attraction of said magnet,and an adjusting screw for tilting said magnet against the magneticattraction on said faces to introduce a wedge-shaped air gaptherebetween.

REGINALD DENNIS SALMON.

